1. Field of the Invention
The invention relates to a flapper type safety valve for subterranean wells and particularly to a pressure equalizing arrangement incorporated in the body of the flapper valve to facilitate the opening of the flapper valve.
2. Description of the Prior Art
Valve mechanisms have been employed in subterranean wells with the primary purpose of effecting a reliable, positive closure of the bore of a production tubing string in the event of any emergency. The actual valving elements of heretofore known valves have comprised ball valves, flapper valves, poppet valves and axially shiftable block elements. Regardless of the type of valving element employed, there has been a problem of effecting the reliable opening of such a valve whenever a significant pressure differential exists between the lower surface of the valve element and the upper surface.
A common form of actuator for a flapper valve is a sleeve which is driven downwardly by a piston shoulder through the imposition of a control fluid pressure supplied from the top of the well head. If a significant pressure differential exists across the flapper valve in its closed position, the amount of force required to be imposed by the actuating sleeve may well cause damage to the sleeve, the flapper valve, or the pivot mounting of the flapper valve. There is, therefore, a need for a pressure equalizing mechanism which accomplishes the equalization of such pressure differential as an automatic consequence of an initial movement of the actuator to open the valve.
Preferably, any type of pressure equalizing mechanism should be simple, reliable, economical to manufacture, and should not result in a significant increase in the diametral dimensions of the tubular conduit in which the flapper valve is mounted. Pressure equalizing arrangements for flapper valves have heretofore been proposed. See for example U.S. Pat. No. 3,799,204 and the co-pending application Ser. No. 259,767 filed May 1, 1981 and assigned to the Assignee of the instant invention. Such prior art equalizing arrangements either involve the incorporation of bypass valves mounted in the tubular conduit or, in the case of the aforementioned co-pending application, involve a pressure equalizing valving arrangement incorporated in the body of the flapper but resulting in a substantial increase in the thickness of the flapper, thus increasing the diametrical dimensions of the safety valve housing in order to accommodate the thicker flapper in its vertical, open position.